1. Field of the Invention
This invention relates to a method and apparatus for fabricating hermetically sealed ceramic integrated circuit packages. In particular, the invention relates to a hermetically sealed ceramic integrated circuit package that efficiently transfers heat from the integrated circuit chip within the package.
2. Discussion of the Related Technology
Military and aerospace applications require highly reliable electronic systems. These systems may be used, for example, in life or death situations such as in jet fighter weapons and life support systems. Critical systems must not have a failure mode that cannot be corrected. If an orbiting space satellite shuts down due to electronic equipment failure, it cannot be repaired. The satellite becomes inoperative and millions of dollars are wasted. Therefore, for these ultra-critical applications, electronic circuits and the packaging thereof must be the finest and most reliable available. Military specifications such as Mil. Spec. 883-B require, among other things, a hermetically sealed package which house an electronic integrated circuit.
Ceramic material is normally used in packaging the integrated circuits to military specifications because of its reliability, heat dissipation characteristics, resistance to vapor and gas penetration, and electrical insulation properties. Fabrication of integrated circuit ceramic packages are well known in the art and have been used extensively in all critical aerospace and military applications. The present ceramic packages are relatively thick, however, and do not facilitate high density packaging or efficient heat transfer from the integrated circuit chip die.
In most military and aerospace applications, no thermal convection cooling of the integrated circuit packages is allowed, all heat transfer must be done by conduction from a substrate away from the integrated circuit package. Conduction of heat from the integrated circuit chip die may be through the metal lead connections or package into the electronic system heat dissipation means such as, for example, a thermally conductive substrate associated with a printed circuit board of the system. Prior art hermetically sealed ceramic integrated circuit packages are large and bulky, resulting in inefficient packaging that is incapable of miniaturization sufficient for today's sophisticated electronic technology. As military weapon systems, such as smart bombs and advanced tactical electronic warfare systems are used in smaller and faster rockets and aircraft, respectively, the need for higher packaging density becomes more critical. Likewise, in space satellite technology, unnecessary size and weight costs dearly during launch and may affect the reliability and useful operating life of the satellite while in orbit.
Packaging techniques for integrated circuit technology are being developed in an attempt to satisfy demands for miniaturization in the semiconductor industry. Improved methods for miniaturization of integrated circuits enabling the integration of millions of transistor circuit elements into single integrated silicon embodied circuits, or chips, have resulted in increased emphasis on methods to package these integrated circuit chips in space efficient, yet reliable and mass producible packages.
An integrated circuit chip is comprised of many interconnected transistors and associated passive circuit elements that perform a function or functions. These functions may include computing, memory data storage, communications, weapons and fire control, etc. Different types of integrated circuit chips are used to create electronic systems to perform specific functions. Combining the functions of different integrated circuit chips requires electrically connecting each integrated circuit chip circuit into the circuits of the system. In order to accomplish this interconnection, conductive paths must be made available to connect the internal circuitry of an integrated circuit chip to the external electrical circuits of the system.
Military specification hermetically sealed ceramic integrated circuit packages may sandwich an integrated circuit chip die and interconnection means between a ceramic or metal element. Various methods of hermetically sealing the ceramic integrated circuit packages are well known in the integrated circuit industry. Either leaded or smaller leadless hermetically sealed package integrated circuit packages bring the integrated circuit chip electrical connections through the ceramic material and to the outer surface of the integrated circuit ceramic package. System electrical connections are made to these external ceramic package connections.